DE 10 2006 052 810 A1 discloses a method for estimating the clamping force that is generated by an electric brake motor in a parking brake of a motor vehicle. The electric brake motor adjusts a brake piston axially against a brake disc and said brake piston is the carrier of a brake pad. The clamping force that is generated as a result is determined by taking into account the current, the supply voltage of the brake motor and also the motor rotational speed using a system of differential equations that models the electrical and the mechanical behavior of the brake motor.
The brake motor is likewise supplied with current in a manner similar to a sequential connection of further electrical consumers by way of the electrical system in the vehicle. If a further consumer is switched on after starting the electric brake motor, the consumer causes a voltage drop and a current drop in the brake motor and said voltage drop and current drop can lead to an incorrect value of the clamping force that is to be determined.
In order to take into account the voltage drop or rather the current drop whilst switching on a further electrical consumer in the case of determining the clamping force, the calculation of a correcting current is disclosed in DE 10 2012 206 226 A1 and said correcting current is used as a basis for calculating the motor resistance and the motor constants that are required to determine the clamping force. The correcting current is determined from a current value that prevails prior to the voltage drop and said current value is modified using a scaling factor.